Gibson served as an SNP councillor in Glasgow for Mosspark from 1992 to 1999, becoming the first ever SNP councillor in the city to serve successive terms. In his second term he secured the biggest majority of Scotland's 1,245 councillors. He was then the sole SNP councillor in Glasgow. Following the defection of three Labour councillors and a by-election win, Kenneth became Leader of the Opposition on Glasgow City Council from January 1998 until being replaced on Glasgow City Council by his mother Iris in the election of 1999.

Within the SNP, Gibson was a Shadow Cabinet front bencher from 1997 to 2003. As SNP Local Government Convenor from 1997 to 1999, Gibson was responsible for writing and producing the SNP manifesto and co-ordinating the parties campaign for the 1999 local government elections.

In 2004, Gibson was 3rd on the SNP's list for election to the European Parliament. In 2007, Gibson was chosen to contest the constituency of Cunninghame North, winning that seat from Labour by the smallest margin in Scotland of 48 votes. In the subsequent 2011 SNP landslide election, Gibson secured a comfortable majority of 6,117 over Allan Wilson, the same Labour candidate, and former Scottish Minister, he had defeated by so slight a margin in 2007.[2]

In addition to his constituency activities, Gibson is also the Convener of the Finance Committee in the Scottish Parliament and has brought attention to enhanced financial powers in the Scotland Act 2012.[3]